Magnetic holding device



Dec. 29 1925.

H. K. SPENCER MAGNETIC HOLDING DEVICE Filed Jan. 29, 1921 fm III. 0

Patented Dec. 29, 1925.

STTES PATENT HENRY K. SPENCER, OF VJATERTOW'N, MASSACHUSETTS7 ASSIGNOR T0 T-EE BLAN- CHARD MACHINE COMPANY, OF CAMBRXBGE, ItIASSAC-EIUSETTS, A CORPORLTION F MASSACHUSETTS.

MAGNETIC HOLDING DEVCE.

Application led January 29, 1921.

T0 all @ch-0m it may concern:

Be known that I, HENRY K. Srnrcsn, a citizen of the United States, and a resident of 'Watertowm in the county of lvliddlesei: and State of llassachusetts, have invented an improvement in lilagnetic Holding llcvices, ot which the following descriptioii, in connection with the accompanying drawings, is a specification, like characters on the drawings representing like parts.

This invention relates to magnetic holding devices, and is more espeially, though not exclusively, concerned with devices ot the type disclosed in ll. El. lietters Patent 1,125,198, issued to me January i9, lfll.

My invention will be bestunderstood )y reference to the following description when taken in connection with the accompanying drawings of one illustrative embocV -nient thereof, while its scope will be more Vparticularly pointed out in the appcn/led claims the drawings:

igure l is a plan, partly in section, magnetic holding device exemphtying my invention g Fig. 2 is a sectional view on an enlarged s -ale on line 2-2 of Fig. l; and

Fig. 3 is a wiring diagram illustrating one w: y of connecting up the coils to a source ot' current.

Referring to the drawings and to the embodiment of my invention which l have lected for exemoliiication, there is shown a magnetic holding device particularly intended ttor use as a rotary chuck, but it should be understood that the invention is susceptible of application to other forms of magnetic holding devices. ln theprescnt c1;- ample the -chuck is provided with a work support t formed of steel or ot1 l ner suitaole magnetic material and provided with a plurality of annular chambers, herein two, designated by the numerals and n". Located in these chambers are sui ible niagnetizing coils l() and l2, respectively. lt should be observed that the work support presents a continuous shell without joints above the coil chambers and hence the coils are protected against the entrance oit' water. D This is 'an important advantage where i desired-'to flood the pieces of work with water while the work is being performed.

The bottoms ont the coil chambers are closed by. platelet formed of suit-able magnetic Serial No. 440,945.

material such as steel and secured work support by appropriate means, herei two sets of screws 16 and 1S.

ln the present example currents et magnitude are passed through the wo coils in opposite directions, as indicated by the arrows in l? B. This creates concentric alternate poles olf opposite polarity, thus causing a magnetic du); to flow around each coil. In the present embodiment the work support extends from pole to pole and the magnetic circuit is complete without the inclusion oit the pieces of work. The latter are attracted and held by making suitable 1rovision for diverting a part otl the magnetic flux from the metallic circuit and compelling the same to flow through the pieces o'r work to be held.

ln the oresent example this accomplished by narrowing the pathoil the magnetic circuit adjacent the work-supporting surface of the chuck by providing the work support with a series of closely spaced concentric grooves, which may be and prei eraloly are lilled with rings of suitable nonmagnetic material, such as brass, designated 20 to 3l inclusive. It should be understood that these rings may be omitted if desired, in which case the grooves will present air gaps performing the same function the rings. The spacing between the bottoms of these rings or grooves and the tops ot the coil chambers is less than the spacing between each coil chamber and the adjacent coil chamber and less than the thickness of metal surrounding the outer coil and thatV which is surrounded by the inner coil.

The metal between the bottoms et the rings or grooves and the tops of the ch hers presents a magnetic shunt fl which a part oli the magnetic ilui; while the remainder is compelled to flow between the rings and into the pieces et wor i An important feature ot my present ini tion relates to the character of this magno shunt. Considering that portion of t shunt which is inmiediately below Aaml or groove, the cross-Sectional a .7 sented i'or the tlow ol the linx is equal to the circumference at that point nir tiplied by the depth of the metal, that is to say, the distance between the bottom of the ring or groove and the top of the coil chamber`4 at the@ reist This baas Se it is widest this C v C ico all if in the case of each ring the thickness of metal below the latter wei'e the same as that which is below every other ring, the shunt would present dilferent cross-sections below the different rings, that is to say, a crosssection of the shunt below the outer ring` would be greater than the cross-section of the shunt below the inner ring because of the difference in diameters. rlhis being so, the holding power of the chuck would be different at each different ring.

In carrying out my present invention this undesirable result is avoided by making the cross-sectional area of the shunt substantially equal beneath all ot the rings or grooves and this is conveniently accomplished by making the top of each coil chamber inclined in an upward and outward direction, as represented in Fig. 2,

that is to say, when considered with relerence to a radial plane, the depth of metal decreases from one ring or groove toward one which surrounds it, or in other words, the cross-section in such plane diminishes in an outward direction to compensate for the increased section in a circumferential direction due to the increase oli' diameter'.

Another important feature of my invention is the provision ol means permitting the use et a less number of coils than heretofore used considered with reference to the holding area of the work-supporting surface. ln the present example, this is accomplished by widening the coil chambers, thereby to spread the magnetic circuit out over a greater number of the spaces between the riz n grooves. This can be safely done within reasonable limits and with very little magnetic leakage by widening the coil chambers at the top as shown at 32 in the chamber 6 and at 34; in the chamber S. lre'i'ierably the side of the chamber (5 is inclined as at and the side of the chainber 8 is inclined as at 3S, thereby to cause the adjacent pole of the magnet to present a relatively thick cross-section. lilith this form there is very little magnetic leakage at the lateral undercut portions of the chambers. 'lhe described construction possesses the advantage of decreased weight and cost ol. mamitacture ot a chuck of a given size with practically the same holding power by the use oit a less number of coils than has heretofore been considered necessary.

The chuck proper may be mounted in any suitable manner and herein is secured to and arried by a driving` gear l0. Rotation ol the gear turns the chuck about a vertical axis which is the center ot the coils as well as the grooves or rings. The coils are connected, one by a lead l2 to a contact ring (lil and the other by a lead /l to a central contact disk 46. These are connected by brushes t8 and 5() and lead wires 52 and to a suit-able source of current 56, The general operation of the chuck should be evident without further description.

Having thus described one embodiment of my invention but without limiting myself thereto, what I claim and desire by Letters Patent to secure is:

l. A magnetic holding device comprising, in combination, a magnetic body having a work-holding face, means associated with the body for producing a magnetic flux to hold magnetic material on said work-holding face, said body providing within itself a complete circuit for the magnetic flux, a portion ot the body adjacent to the workholding tace, and within the circuit, constituting a magnetic shunt, said portion ha ving a varying thickness, said body presenting at intervals recesses separated by magnetic connections leading from said shunt portion to said face, thereby to divert a part ot the magnetic flux from the magnetic circuit and to compel the same to flow through the magnetic pieces to be held while the remaining flux flows through said shunt portion.

2. A magnetic holding device comprising, in combination, a magnetic body having a work-holding face, means associated with the body for producing a magnetic llux to hold magnetic material on said work-holding` face, said body provii'ling within itself a complete circuit for the magnetic ilux, a portion of the body adjacent to the workholding tace and within the circuit constituting a magnetic shunt, said shunt portion having' a thickness which tapers along said work-holding face and said body having provision to divert part of the magnetic linx from the i'nagnctic circuit and to compel the same to How through the magnetic pieces to be held while the remaining flux flows threugh said shunt portion.

3. A magnetic holding device comprising, in combination, a magnetizing coil, and a magnetic body having a work-holding face, forming within itself a complete magnetic circuit for the magnetic ilux from said coil, the work-holding face of said body having a plurality ol recesses to reduce the cflective cross-sectional area of the magnetic mass at a portion of the magnetic circuit, thereby to compel a portion ot the lines of vforce to pass into the material held, the latter thereby `forming a part of the magnetic circuit, that portion of the body Within the complete circuit and adjacent to said work-holding` face, providing a shunt, and tapering along said work-holding face.

-l-. A magnetic holding device comprising, in combination, a body of magnetic material presenting a work-holding face, a magnetic coil associated with said body, said body forming within itself a complete magnetic circuit about the cross-section ot said coil, a portion of the body within said circuit lying'adjacent to the work-holding face and presenting a substantially uniform cross-section to the path of the iux.

5. A magnetic holding device comprising, in combination, a magnetizing coil in the form of a ring, and a body ot magnetic material presenting a Work-holding face transverse to the axis ot said ring, said body presenting a chamber in Which said coil is received and providing Within itself a complete magnetic circuit about said chamber, the thicknesses of that portion of the body intermediate said chamber and said Work-holding face at different radial distances from said axis being approximately inversely proportional to the circumferences at such points.

6. A magnetic holding device comprising, in combination, a magnetizing coil, and a body of magnetic material having a Workholding face and provided With a chamber in which said coil is received, said body presenting Within itself a complete circuit for the magnetic iiux, a portion of the body adjacent to the Work-holding face, and Within the circuit, constituting a magnetic shunt, said body presenting at intervals recesses separated by magnetic connections leading 'from said shunt portion to said face, thereby to Vdivert a part of the magnetic tlux from the magnetic circuit and to compel the saine to flow through the magnetic pieces to be held, While the remaining liux flows through said shunt portion, the area ot said face served by said recesses being substantially greater than the corresponding area of said coil, and said chamber being substantially Wider than the corresponding dimension of said coil adjacent to said tace, thereby to compel lines of torce to flow between the recesses Which are outside of said area of said coil.

7. A magnetic holding device comprising, in combination, a magnetizing coil, and a body of magnetic material having a Workholding Jface and provided With a chamber in Which said coil is received, said body presenting Within itself a complete circuit for the magnetic flux, a portion of the body adjacent to the Work-holding face; and

Within the circuit, constituting a magnetic f shunt, said body presenting at intervals recesses separated by magnetic connections leading from said shunt portion to said tace, thereby to divert a part of the magnetic flux from the magnetic circuit and to compel the same to flow through the magnetic pieces to be held, While the remaining flux Hows through said shunt portion, the area ot said face served by said recesses being substantially greater than the corresponding area of said coil, and said chamber having a Width approximating the corresponding dimension of that portion of said face Which is served by said recesses, thereby to compel lines of force to flow between the recesses which are outside ot said area of said coil.

8. A magnetic holding device comprising, in combination, a magnetizing coil in the form of a ring disposed about an axis, and

body of magnetic material having a Workholding face and provided with an annular chamber in Which said coil is received, said body presenting Within itself a complete circuit for the magnetic flux, a portion of the body adjacent to the Work-holding face, and

Within the circuit, constituting a magnetic shunt, said body presenting annular recesses about said axis, thereby to direct a part of the magnetic flux from the magnetic circuit and to compel the same to flow through the magnetic pieces to be held, While the remaining flux flows through said shunt portion, the area of said face served by said annular recesses being substantially greater than the corresponding annular area ot said coil and said annular chamber having a radial dimension greater than the corresponding dimension of said coil adjacent to said Jface, thereby to compel lines oi" vforce to HOW between the recesses which are beyond the area of said coil.

In testimony whereof, I have signed my name to this specication.

HENRY K. SPENCER. 

